1. Field of the Invention
The present invention relates generally to a variable speed transmission of the belt-pulley type wherein the V groove of the driving pulley is capable of varying in width to increase or decrease the speed of the driven pulley, connected to the driving pulley by the belt, by displacement of the latter in the V groove.
2. Description of the Prior Art
In a variable speed transmission of the above general type, as used on snowmobiles, motorcycles and other like utilitarian or recreational vehicles, the pulley comprises a pair of V groove-defining cheeks rotatable in unison about a common axis and of which one is axially stationary while the other is axially movable. Located on the side of the pulley away from the stationary cheek is a reaction cup which is also axially stationary by being made solid with the said stationary cheek, for instance. The movable cheek and the reaction cup are formed with conical cam surfaces converging toward one another and defining between them a chamber into which are housed a set of centrifugal weights having the shape of an isosceles trapezium in cross-section. The weights are free to move radially away from the common axis and are slidable along their conical cam surfaces. As the centrifugal force of the weights increases with increasing speed of the driving pulley, driven by the motor, the weights move radially outward and force the movable cheek toward the stationary one to narrow the V groove between them, causing the belt to climb in the groove thereby increasing the speed of rotation of the driven pulley or, more generally, varying the speed ratio between the driving and driven cheeks.
The generating lines of the conical cam surfaces being rectilinear, the spreading movement of the cheeks is proportional to the radial displacement of the centrifugal weights.
The best prior art reference known to Applicant, with respect to his invention, is French patent application No. 2,504,635, in the name of Carnot and published on Oct. 29, 1982. In this application, the centrifugal weights used are in the form of spheres providing a pin-point contact between the spheres and the cam surface of the reaction cup. In Applicant's transmission, the improved centrifugal weights and reaction cup are shaped to provide surface contact between them resulting in reduced and more evenly distributed wear, as will be seen hereinafter. Moreover, in the Carnot application, the contact point between the spheres and the cam surface is always at the same distance from the center of gravity of the spheres, because of their shape. In Applicant's transmission, the distance between the contact point of the weights and their center of gravity varies as a function of the position of these weights. As a result, the resultant of the forces applied by the weights onto the cam surface also varies and may be selected to meet some specific requirement (e.g. clutch response).
Other patents known to Applicant are:
U.S. Pat. Nos.:
2,378,549
2,512,816
3,230,787
3,850,050